CODEWITHSUNDEEP
javadesign-patternsfactorybuilder
Richard B
Richard B

Reputation: 935

Understanding the Builder/Factory Pattern

I'm trying to clean up some code I have written for reading data. I have two sources of data: a database and a file. Both currently have separate classes and both classes have optional, non common, parameters in the constructors provided (at the moment traditional telescoping constructors).Both classes Implement interface MyData and when I instantiate the objects I always instantiate a MyData object.

I want to merge these classes into a single class and make the instantiation as clean as possible but I can't figure out how. Im certain its a mixture of builder and factory patterns.The user should never have to see the underlying type MyDatabaseData and MyFileData, just MyData. Can someone help me by sketching out a similar example just to set me off in the right direction

Upvotes: 0

Views: 335

Answers (2)

Joop Eggen
Joop Eggen

Reputation: 109547

A builder pattern would look like this:

MyDatabaseData data = MyDatabaseData.create()
       .authenticate("admin", "rumpelstielchen")
       .get();

public class MyDatabaseData {
    private MyDatabaseData() { }
    public static MyDatabaseBuilder create() {
        return new MyDatabaseBuilder(new MyDatabaseData());
    }
}

public class MyDatabaseBuilder {
    private MyDatabaseData data;

    MyDatabaseBuilder(MyDatabaseData data) {
        this.data = data;
    }

    public MyDatabaseData get() {
        return data; // Do checks and yield the final result
    }

    public MyDatabaseBuilder authenticate(String user, String password) {
        ...
        return this; // For chaining calls
    }
}

Whether to use common base classes/interfaces is a matter of suitability:

public class MyDatabaseBuilder extends MyBuilder<MyDatabaseData>

However you will probably need to do specific things and hence need child classes. Development not necessarily will become easier, maintaining 4 classes with parallel evolutions.

Upvotes: 0

dkatzel
dkatzel

Reputation: 31648

Keep the classes separate since they do different things. Combining them will only make a giant mess and violates the Single Responsibility Principle.

If you don't want the users to see the classes, then make the classes package private.

Then you make a new Builder or Factory class that takes parameters and figures out which class to instantiate.

Hope this helps.

Upvotes: 1

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